IMO one livestock dog does fine as long as she doesn't have a lot of animals or a large area to patrol. They are smart enough to retreat when they get in over their head. It would be wise, I agree to let the dog gets used to it's new home then get a pup for it to train. I certainly wouldn't put a pup in with a dog that wasn't at home yet. If you have two dogs they work as a pair. One usually works the outside area while the other works up close to the animals. If one or the other has a big problem they have a certain bark and the second one will come running to assist. However if you don't have a lot for them to watch and you have two dogs they can easily get bored and that is when they might start wandering some. A pup along with an older dog to train it is the perfect set up in my opinion. The older established dog will train the pup and it keeps them both occupied. If I were you Josie, I would ask the people you are getting the dog from where they got their dog. There is an outstanding GP breeder in the LeRoy area with huge dogs that are known for their excellent abilities. Unfortunately I don't know what their name is and the person I could ask if off work on medical leave right now so I have no way to contact them for the information.
People will argue till they are blue in the face about LGD. But the one true thing I think everyone agrees on is there is no dog better suited all around for livestock as well as poultry than a Great Pyrenees. They are beautiful, smart, loyal and majestic.
Agree totally!